The invention relates to a container, comprising a body, made of thermoplastic material, and end walls, at least one of which is made of a thermoplastic material, said body and end wall being butt-welded to each other with flat weld faces lying at right angles to the axis of the body, the weld face of the body being of a width which prior to welding is essentially equal to the wall thickness of the body, while the weld face of the end wall is of a width which is greater than the width of the weld face of the body and has an external diameter which is greater than the external diameter of the body, and said end wall has an axially and radially outward-facing flange which forms a gripping edge.
Such a container is known. In this known container the body and one or both end walls are welded to each other by means of so-called heated-tool welding, i.e. welding in which the faces to be welded to each other are brought to welding temperature by means of a hot plate, the heated tool, following which the plate is removed and the two heated weld faces are pressed together and fused. The heated tool is a plate which is flat on both sides. Only those faces of body and end wall which are to be welded to each other may be brought into contact with this tool. In the case of the body this is no problem, because it is a continuous cylindrical tube. However, the end wall is more complex in shape, in particular due to the fact that there must be a gripping edge which makes it possible to take hold of the container, not only by hand, but in particular with a gripping device designed for the purpose, which can grip the gripping edge at two opposite faces. During handling with a gripping device, the gripping edge and the place where the material passes from the gripping edge to the end wall must be sturdy. Besides, the gripper must not grip the weld point. All this means that in the case of the known container the weld face of the end wall is located inwards from the innermost face of the gripping edge, viewed in the axial direction. On account of these considerations, the transition from an end wall to the gripping edge, situated near the weld point, has a large volume of material. This volume is at the end of the flow path of the liquid plastic in the injection mould. With the known form of gripping edge, the stream of liquid plastic has to divide during injection moulding into a stream going to the hollow for the gripping edge and a stream going to the part which forms the weld face of the end wall after setting of the plastic.
The face which is going to form the weld face is an end face for the flow front. This and the preceding dividing, which gives rise to eddies, results in shape inaccuracies when the plastic material is contracting and shrinking during cooling, and while these types of inaccuracies do not prevent a good welded joint from being obtained, they can extend the welding time.
This known container is of excellent quality and meets all the international strength and safety standards laid down by law, but it does have a number of disadvantages and, if they could be eliminated, an even better container would be produced. For example, the welded seam is ugly, while the bottom gripper can glance off the weld and then no longer properly grips the face intended for the gripper. The concentricity of cover and body can have a slight deviation of about 1.5 mm, but the consequence of this is that the weld face of the end wall has to be wider than the weld face of the body, for locally the body can be fused more inwards or more outwards with the weld face of the end wall.
It is known to mill away the weld edge partially in order to improve the appearance and produce a better grip for the gripper. If the weld edge locally is far inwards, then a part of the section of the end wall connecting to the weld has to be milled away, which is at the expense of the strength.